The present invention relates to a vehicle air conditioning system for use in a so-called idle-stop vehicle having an engine stopped when the vehicle in a running state comes to a temporary halt.
So-called idle-stop vehicles have recently been introduced for saving fuel. Since, such an idle-stop vehicle stops the engine when the vehicle comes to a temporary halt, the air-conditioning compressor, which is driven by the engine, and a mechanical pump for a heating unit are stopped, and the air-conditioning system does not operate while the engine is stopped.
To prevent this, Japanese Patent Laid-Open Publication No. 2000-130323 discloses technology associated with a hybrid compressor provided integrally with an electric motor. When the engine is stopped, the compressor is operated by the electric motor to compress refrigerant, thereby operating a cooling unit.
On the other hand, Japanese Patent Laid-Open Publication (JP-A) No.(Hei) 9-277818 discloses the provision of an electric pump and a bypass channel in the cooling water circuit of a heating unit. When the engine is stopped, the heating unit is operated by driving the electric pump.
These devices allow the operation of either the cooling unit or the heating unit when the engine is stopped.
However, the devices disclosed in these publications are insufficient if the air-conditioning system is assumed to perform both cooling and heating functions throughout the year in an idle-stop vehicle.
If the devices are used in combination, both the cooling and heating functions can be performed satisfactorily. However, this increases the number of parts, resulting in a complicated and very costly system.
In another proposed solution to this problem, Japanese Patent Laid-Open Publication (JP-A) No. 2000-127753 discloses the provision of an electric compressor driven by a battery-powered motor in addition to the compressor of a cooling unit. During a stoppage of the engine, the cooling unit is operated by the electric compressor so that cooling is performed, regardless of whether the engine is running or at rest.
The motor is activated when the engine comes to a stop, and continues operating while the engine is stopped. Consequently, the battery may be overtaxed, which may result in insufficient battery strength the next time the engine is started, and the life of the motor may be too short.
In a further proposed solution, as described in Japanese Patent Laid-Open Publication (JP-A) No. 2000-80348, some systems reduce the load on the motor that operates when the vehicle and engine are stopped. Specifically, the operation of the motor is combined with controls such that an air mix door is fixed to a full cool position or fixed in an inside air circulation mode, and an evaporator anti-freezing temperature is raised by a predetermined value.
Also, when a vehicle stops temporarily, since the compressor intended for the cooling unit and the mechanical pump intended for the heating unit are also stopped, the air-conditioning systems do not operate while the engines are stopped.
As means for solving this problem, Japanese unexamined patent publication (JP-A) No. 2000-127753 has disclosed the provision of an electric compressor driven by a battery-powered motor to assist the compressor of a cooling unit. During an engine stoppage, the cooling unit is operated by the electric compressor so that the cooling function is performed regardless of whether the engine is running or at rest.
The motor is activated when the engine comes to a stop, and continues operating while the engine is stopped. Consequently, the battery capacity may fall to the extent that there is insufficient battery capacity the next time the engine is started, and the life of the motor is in doubt.
As described in Japanese Patent Laid-Open Publication No. 2000-80348, some proposals reduce the load on the motor. Specifically, the operation of the motor and the control of other devices is such that, when the motor operates, an air mix door is fixed to a full cool position or fixed in an inside air circulation mode, and such that an evaporator anti-freezing temperature is raised by a predetermined value.
As a consequence, the compressing load is reduced in comparison to that when the engine is running, so that the compressor consumes less power, which reduces the load on the motor. The battery power supply is thus prevented from extraordinary draining.
While such proposals can reduce the power used by the compressor under steady use conditions, variations are naturally expected in the cooling conditions, the frequency of engine stops during moving, and so forth depending on the passengers. Operating the compressor accordingly even under such unsteady conditions as higher cooling loads and longer engine stop times may overtax the battery. In short, the battery may be exhausted.